Pulsed oscillator



Dec. 9, 1947. H. J.QDAILEY Ef L 2,432,227

PULS ED OSCILLATOR Filed Aug. 24, 1945 VOLTS TIME Pulse Generator ATTORNE Patented Dec. 9, 1947 UNITED STATES PATENT OFFICE PULSED OSCILLATOR Application August 24, 1943, Serial No. 499,784

2 Claims.

Our invention relates to circuits for radio transmission and, in particular, relates to an arrangement for protecting apparatus used in such circuits from destructive effects resulting from arc-over in transmitter tubes when steep voltage pulses are impressed on their input circuits.

For certain purposes in modern radio systems,

it is desirable to provide oscillation generators which produce output current only in short pulses or wave groups separated from each other by intervals of zero output. One arrangement for this purpose is that electronic tubes having control electrodes are arranged in the well known manner so that energy feed-back between their output and control electrode circuits will cause them to generate oscillations except when their control electrodes are biased sufficiently negative relative to their cathodes. By then impressing on the control electrodes a voltage of the general wave form, shown in Fig, 1 of the drawings, in which the control electrode is maintained at substantial negative potential relative to the cathode during the intervals in which zero output from the generator is desired, and rises sharply to a slightly negative, or even slightly positive, potential for the brief intervals during which it is desired that the tube generate oscillations, the above-described operation of the oscillator gen erator is attained.

However, in practical use it is found that the impression of such sudden pulses of potential on the control electrodes has a tendency to cause occasional arc-overs between the control electrodes and the anodes; and when this happens apparatus connected in the control-electrode circuits may be ruined.

One object of our invention is, accordingly, to provide a protective arrangement for oscillation generators operating in the above-described manner, which shall prevent accidental arc-over from the anode to the control electrode from raising the potential of the grid bias supply to high positive values.

Another object of our invention is to provide an arrangement for oscillation generators of the above-described type, in which the flow of destructive currents to the control-electrode circuit from other electrodes in the tube is prevented.

Other objects of our invention will become apparent upon reading the following description, taken in connection with the drawings; in which:

Figure 1 is a graphical plot of the wave form of the voltage impressed on the control electrode relative to the cathode of the tube shown in Fig. 1.

Fig. 2 is a schematic diagram of a circuit embodying the protective arrangement in accord ance with our invention; and

Fig. 3 is a schematic diagram of an alternative arrangement for a part of the circuit of Fig. 2.

Referring in detail to Figure 1, abscissas represent time, while ordinates below the horizontal zero line represent negative potential impressed on the control electrode circuit by the keying circuit relative to the cathode. Such a wave form is seen to represent periods of a strong negative potential intervening between sharp pulses of more positive potential.

Referring in detail to Fig. 2, the rectangle 2 schematically represents an electrical generator of pulses having the wave form shown in Fig. 1, the negative terminal of this generator being connected to ground. Such generators are well known in the radio art and need no detailed description here. The positive terminal of this generator is connected by a network, about to be described, to the controlelectrode 3 of an electron tube i, which may, for example, be a triode of high vacuum hot cathode type. The cathode of the tube 4 is connected to ground and its anode is connected through an anti-resonant circuit comprising an inductance 5 and a variable capacitor 5 to one terminal of a choke coil 1, the other terminal of which is connected to a positive source of voltage, the negative terminal of which is grounded. The common terminal of the above-mentioned anti-resonant circuit 5, t and the choke coil 1 is connected through a capacitor 8 to ground.

The control electrode 3 of the tube 4 is connected through a second anti-resonant circuit comprising an inductance H and a variable capacitor T2 to the ungrounded terminal of the pulse generator 2. The inductance H and the inductance 5 are positioned in mutual inductive relation with each other. The terminal of the inductor H and capacitor 52, which is remote from the control electrode 3, is connected to the cathode of tube 4 through a capacitor l3. It will be readily evident to those skilled in the art that the circuits of the tube t will cause it to generate electrical oscillations at a frequency determined by the settings of the anti-resonant circuit 5, 6 and II, l2. It will also be evident that the pulse generator 2 will normally maintain the control electrode 3 of the tube 4 at a potential negative to the cathode of tube 4 by an amount represented by the lower portion of the graph in Fig. 1, but will at intervals raise the potential of the control electrode 4 to values only slightly negative relative to the cathode in correspondence with the short pulses appearing in the graph in Fig. 1.

By proper adjustment of the magnitude of the crest and troughs of the current wave represented by Fig. 1, the tube 4 can be caused to produce no oscillations except during the short intervals represented by the crests of the waves in Fig. 1.

As previously stated, it is found in practice that there is a tendency for arc-over to occur between the anode and the control electrode of tube 4 during some of the voltage pulses represented by Fig. 1. When this occurs, the control electrode is likely to be raised momentarily to the full positive potential of the anode of tube 2. This usually has a very destructive effect on apparatus connected in the control-electrode circuit,

In order to avoid the possibi ity of raising the potential of the control electrode 3 to the relatively high value of the anode of tube 2, we

connect, across the terminal of the pulse gener-' ator 2, a rectifier M which may, for example be diode 2 having an anode and a thermionically emissive cathode. The tube 14 may, if desired, be provided with a gaseous atmosphere although a high vacuum tube may also be suitably used under certain conditions which will be evident to those skilled in the art. With the tube id present in the circuit, any tendency for the control electrode 3 to become substantially positive relative to the cathode of tube 4 will cause a rapid discharge of current through the tube I4, this tube, in effect, preventing any rise of th control electrode 3 to a substantial positive potential relative to the cathode 2 of tube 4. This prevents the flow of substantial grid currents from the said cathode to the control electrode 3 and eliminates any destructive overheating of the control electrode and its supports.

While I have described the rectifier M as a diode, other types of rectifier may be substituted therefor, for example, the tube It may comprise a spark gap between two principal electrodes hav ing in the space between them a third electrode which will prevent passage of current between the principal electrodes, except when the control electrode is positive.

To take another example, a thyratron comprising a, thermionically emissive cathode and anode and a grid electrode may be used, the grid electrode preventing current fiow between the anode and cathode, except when the grid electrode is rendered more positive than the cathode by arcover between the anode and the control electrode of tube 4.

To take still another example, an electrolytic condenser may be substituted for the tube 1 4 with the condenser connected with the proper polarity so that it readily passes positive charges from the control electrode 3 to ground, but is substantially of high impedance to flow of positive charges in the opposite direction.

Referring in detail to Fig. 3, rectifier l4 and the line connecting the ungrounded terminal oi pulse generator 2 to the anti-resonant circuit I I, I2 in Fig. 2 may be replaced by the choke coil 2 l, the ignitron 22, and the capacitor 23 of Fig. 3.

Any tendency of the control electrode 3 of tube 4 to become positive relative to the cathode of tube 4 will cause the transmission of an impulse to ground through capacitor 23 and impedance 24. The igniter electrode 25 of tube 22 will, therefore, be traversed by a corresponding current pulse which will initiate an are between the principal electrodes of the ignitron 22, causing the latter to discharge current flowing through the grid 3, and. to maintain it at substantially the potential of the cathode of tube 6. When the pulse generator 2 again makes the potential of control electrode 3 strongly negative relative to the cathode of tube 4, the current flow through the ignitron 22 will cease, and the later will then remain non-conductive until another arc-over occurs between the anode and control lectrode of tube 4.

While I have described a specific embodiment of the principles of our invention, these principles are capable of embodiment in many other forms which will be evident to those skilled in the art.

We claim as our invention: 1. In combination, an electrical discharge tube having a cathode and an output circuit and an input circuit associated with said cathode, a.

source or" voltage for the output circuit, an antiresonant circuit connected in one of said output circuits, a feed-back of energy between said output and said input circuit, a pair of serially connected impedances in said input circuit, a generator adapted to impress a voltage wave which is strongly negative, except for periodic, more positive pulses on said input'circuit, and a rectifier connected in shunt with the one of said impedances which is nearer to said cathode, said rectifier having its negative terminal connected directly to the cathode of said tube.

2. In combination, an electrical discharge tube having a cathode with an output circuit and an input circuit associated with said cathode, a source of voltage for the output circuit, an input electrode connected to one side of said input circuit, an anti-resonant circuit connected in at least one of said circuits, means for producing a feedback of energy between said output and said input circuit, an impedance in said input circuit, a generator adapted to impress a voltage wave which is strongly negative, except for periodic, more positive pulses on said input circuit, and a rectifier having one terminal directly connected to said cathode, and its opposite terminal connected to said one side of said input circuit, the terminal of said rectifier connected to said cathode being the negative terminal.

HAMPTON J. BAILEY. CARL H. SCULLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,695,042 Fearing Dec. 11, 1928 1,857,128 Acheson -1 May 10, 1932 1,971,383 Prinz Aug. 28, 1934 2,153,172 Buschbeck 1 Apr. 4, 1939 2,181,568 Kotowski et al Nov. 28, 1939 2,198,850 Andrieu et a1. Mar. 19, 1940 2,205,233 Van Slooten June 18, 1940 2,225,046 Hunter Dec. 17, 1940 2,237,661 Ernst Apr. 8, 1941 2,250,706 Geiger July 29, 1941 2,417,834 Lord Mar. 25, 1947 

